GRE

Generic Routing Encapsulation (GRE)

• IP Protocol 47
  • In the IP header there is a protocol field
• Tunnel interface
  • If a router does IP and does GRE you can create a tunnel between two sites anywhere on the internet
  • "The network duke tape"
• Point-to-point & multipoint support
• Supports non-IP traffic
  • Wherever I go I can get internet access and as long as I have internet I can create a GRE tunnel
  • No encryption and no authentication
  • Weird scenarios where we have no IP traffic
• "User defined pipe" over IP

Generic Encapsulation

• "Just a box"
• Any payload
• Any destination
• No encryption
• Typically processed in software
  • Software function that runs in your CPU
  • Constantly interrupting the general purpose CPU to perform that function.
  • Example:
    • CPU - Generic
    • GPU - Blazing fast
    • ASIC - This is why switches are fast
  • Impacts how that router is going to run